Packaging and details of a wireless power device

ABSTRACT

A wireless power system includes a power source, power receiver, and components thereof. The system can also include a parasitic antenna that can improve the coupling to the power source in various modes. The antenna can have both a variable capacitor and a variable inductor, and both of those can be changed in order to change characteristics of the matching.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/398,179, filed Mar. 4, 2009, which claims the benefit of U.S.Provisional Application No. 61/034,116, filed Mar. 5, 2008, both ofwhich are hereby incorporated by reference in their entireties.

BACKGROUND

The number of battery powered electronic devices and gadgets used indaily life is steadily increasing. Important such devices include:

-   -   Communications handsets: mobile phones, cordless phones    -   Infotainement: Music (MP3) players (diskman, ipod, etc.), Mobile        TV, portable audio    -   broadcast receivers    -   Photo/video: Digi/video cams    -   Wireless peripherals: Bluetooth headsets, cordless microphones,        etc.    -   Time & navigation: wrist watches/computers, GPS devices    -   IT: PADs, Laptops, cordless keyboards & mice, etc.    -   Household: Electronic clocks, thermometer, weather stations,        pocket calculators, etc.    -   Medical: hearing aids, cardiac pacemakers, etc.    -   Sport: stopwatches, avalanche beacons, bike computers, bike        lamps, pocket lamps,    -   pulse monitors, etc.

Wireless communications has brought certain freedom from wires for thecommunication. However, recharging of those devices still requireswires. Many other electronic devices use non rechargeable batteriesrequiring frequent replacement producing an environmental burden. Tomake matters worse, there is no true standard charging interface. Manydifferent re-chargeable devices require their own wall charger.

Battery technologies have improved, but Personal Electronic Devices(PEDs) in average are getting more power-hungry due to added featuresand increased usage (e.g. mobile phone with integrated digicam, colourscreen, gaming and MP3 players), thus effectively resulting in reducedinstead of expanded autonomy time.

Getting power to portable devices has been the focus of a series ofrecent products that attempt to resolve traditional chargingfrustrations. This includes wind-up chargers, zinc-air power packs, USBchargers and multi-tipped universal chargers. These form niche marketsectors, but none has met with widespread success.

Our previous applications and provisional applications, including, butnot limited to, U.S. patent application Ser. No. 12/018,069, filed Jan.22, 2008, entitled “Wireless Apparatus and Methods”, the disclosure ofwhich is herewith incorporated by reference, describe wireless transferof power.

The transmit and receiving antennas are preferably resonant antennas,which are substantially resonant, e.g., within 10% of resonance, 15% ofresonance, or 20% of resonance. The antenna is preferably of a smallsize to allow it to fit into a mobile, handheld device where theavailable space for the antenna may be limited. An embodiment describesa high efficiency antenna for the specific characteristics andenvironment for the power being transmitted and received.

One embodiment uses an efficient power transfer between two antennas bystoring energy in the near field of the transmitting antenna, ratherthan sending the energy into free space in the form of a travellingelectromagnetic wave. This embodiment increases the quality factor (Q)of the antennas. This can reduce radiation resistance (R_(Γ)) and lossresistance (R₁).

In one embodiment, two high-Q antennas are placed such that they reactsimilarly to a loosely coupled transformer, with one antenna inducingpower into the other. The antennas preferably have Qs that are greaterthan 1000.

SUMMARY

The present application describes use and applications of wirelesspower.

Aspects include tuning of wireless antennas, and packaging of thoseantennas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an energy transmitter for wirelesscontrol;

FIG. 2 shows a block diagram of the energy receiver for wireless power;

FIG. 3 shows a generic energy relay, parasitic antenna and repeaters;

FIG. 4 shows a wireless desktop for a computer;

FIG. 5 shows coplanar magnetic field coupling between the desktopdevices;

FIG. 6 shows a wireless device in a wireless charging station;

FIG. 7 shows a first embodiment of a wireless charging station;

FIG. 8 illustrates the principle of the first embodiment.

FIG. 9 shows a wireless charging station and portable device accordingto a second embodiment;

FIG. 10 shows a third embodiment of the wireless charging station;

FIG. 11 shows an embodiment of a wireless power bridge;

FIG. 12 shows another embodiment of a wireless power bridge;

FIG. 13 shows the transmit subsystem for the wireless power device;

FIG. 14 shows the antenna used in the wireless power device;

FIG. 15 shows the receive subsystem for the wireless power device;

FIG. 16 shows one embodiment of a circuit for varying the tuning of theantenna;

FIG. 17 shows another embodiment of a circuit for varying the tuning ofthe antenna;

FIG. 18 shows another embodiment of a circuit for varying the tuning ofthe antenna;

FIG. 19A shows another embodiment of a circuit for varying the tuning ofthe antenna;

FIG. 19B shows another embodiment of a circuit for varying the tuning ofthe antenna;

FIG. 20 shows another embodiment of a circuit for varying the tuning ofthe antenna;

FIG. 21A shows a cross sectional view of an embodiment of a ferriteantenna depicted above a side view, the views showing another way ofvarying the tuning of the antenna;

FIG. 21B shows another side view of the embodiment of FIG. 21A;

FIG. 22 shows electronic resistance;

FIGS. 22A-22B show integration of in the antenna loop into a cover orkeyboard part; and

FIG. 23 shows a multiple receiver scenario.

DETAILED DESCRIPTION

People typically just want to use electronic devices and do not want toworry about charging them. For most people, charging and replacingbatteries have become another chore in their day-to-day routines.

People need to remember to change their batteries and also to have theright charger at hand. They need to free up wall sockets to plug in.Discharged batteries lead to unreliability of phones, mice andkeyboards. To charge multiple devices, users carry multiple differentchargers and cables.

The inventors recognize a need for a sustainable infrastructure that canbe used commonly as a standard. A universal standard for poweringportable devices could have huge benefits to both consumers and to OEMs,the latter of whom could reduce prices by omitting chargers when theysell their products.

Establishing a universal power standard has in the past been constrainedpartly by the mechanics of device connectors or charging contacts. Thesecan vary among devices. Different devices may also have different powerrequirements.

Wireless power as defined by this application can sidestep many of theseissues. An embodiment describes inductive coupling based on time variant(AC) magnetic fields. Wireless power avoids wires, connectors orcontacts between the powering station and the device. Another advantageis that this system provides hermetically sealed (waterproof) electronicdevices. This solution can charge multiple devices with different powerrequirements, all at the same time.

Wireless power technology can create a new infrastructure so that peoplehave opportunities to recharge their electronic devices in sharedlocations. Anyone within a zone could recharge, without the need formultiple chargers. A wireless charging zone may be in a friend's house,a cafe, restaurant, hotel or airport lounge. Wherever people go, theywould know that they can re-power all their devices.

The generic wireless energy source consists of the following subsystemparts and functions as shown in FIG. 1. A power supply 100 receives asource of power, e.g., from a wall socket. This is used to modulatepower on an RF power source 110, that produces power at a specified RFfrequency. A matching circuit 120 matches the RF output to the resonantantenna 130, to minimize the impedance mismatches. The antenna mayitself have tuning 140 and orientation control 150 that can controlcharacteristics of the transmission.

A control system 160 controls the operation. A wireless interface 170may couple the wireless power.

Each of these subsystems is described in detail herein.

The power supply 100, can generally be a high efficiency switched-modepower supply to produce a DC voltage to drive the RF power stage 110.Very high conversion efficiencies (>95%) can be achieved. Depending onapplication, an AC/DC converter or a DC/DC converter (e.g. forautomotive applications) may be used. For the transmitter's own controlfunctions, a constant voltage but low wattage may also be used, e.g., a5v or 12V supply.

In special solutions/applications the power supply may be omitted or maybe only a rectifier.

An adaptive system may adaptively control this voltage level using thecontrol system 160.

The RF power source 110 maybe a non-linear high-efficiency power stageusing power switches (Transistors, FETs, etc.) driven by a square waveoscillator. For vicinity coupling systems operated with higher magneticfield strength the use of a frequency reference, such as generated froma crystal oscillator, may be preferable with respect to frequencyregulatory issues. A common frequency may be defined on an internationalbasis for such applications e.g. at

-   -   13.56 MHz (ISM-band) in the HF band    -   around 135 kHz (ISM-band) in the LF band

Frequency generation may however be considered as part of the controlsystem.

For transmitters operating in the VLF/LF range, a power efficienthalf-bridge ‘inverter’ circuit is typically used. This stage may bemodeled by a low impedance source (voltage source) with a rectangularwaveform, although this can alternatively be any other kind of waveform.

The antenna current as generated by the rectangular voltage waveformwill be smoothed by the resonant antenna circuit into a sinusoid. Theresonant circuit may inherently suppress harmonics emissions.

In certain cases, however such as a receiver with close proximitycoupling, the loaded Q-factor may become so low that there is nosignificant wave shaping effect. This increases the bandwidth of thedevice. In such case however, lower harmonic radiation would be expectedsince antenna currents on transmitter and receiver will drop to lowlevels also partially compensating themselves. To a certain extent,harmonic radiation potential and the wave shaping effect are related, sothat harmonic radiation may always be kept below any unwanted emissionlimits.

Power and efficiency control maybe accomplished through changing the DCsupply power and/or the duty cycle of a signal, e.g., a square wave,driving the ‘inverter’.

In one embodiment, an antenna matching system is used.

In another embodiment, no specific antenna matching circuit may berequired in the transmitter. Assuming a loop/coil antenna the use of acapacitor as an anti-reactor to compensate for the inductive reactanceof the loop/coil may be sufficient to compensate. The output of the lowimpedance RF power source may be directly connected to the resonant tankcircuit (series resonant circuit). To preserve high efficiency, thisrequires the source impedance (resistance) of the RF power stage to beconsiderably lower than the resonance resistance of the tank circuit,such that only a small percentage of generated power is dissipated inthe source resistance. The source-to-resonance resistance ratio may becontrolled to a certain extend through antenna design parameters (L/Cratio).

The system also uses a resonant antenna 130. In a magnetically(inductively) coupled system, the antenna is generally a multi-turn loop(coil). At higher frequencies, single turn loops may be used. Theantenna coil may be designed to withstand the high voltages and currentsresulting when the transmitter subsystem is unloaded, e.g., when noreceivers are within range. It must provide a Q-factor as high aspossible since this Q-factor will limit transfer efficiency at thefringe of service coverage and range.

It is expected that in a practical system implementation, Q-factors upto 300 are achievable at LF and up to 600 in the HF frequency range(13.6 MHz). In non-integrated laboratory samples Q-factors twice as highmay be achievable.

Copper tube or silver plated copper tube may be adequate material tobuild a HF loop. At LF, thin well insulated wire or thicker strandedwire (litz wire) may be used, depending on the targeted L/C ratio andthe power rating. At LF, the antenna coil may provide taps for matchingor tuning purposes. At HF, the use of a special coupling loop/Coil(acting as an up-transformer) may be used to match to the impedance ofthe antenna and prevent loading effects from the circuit.

Assuming a fixed and defined operating frequency, e.g, a frequency thatis crystal controlled, tuning of the resonance frequency antenna cancompensate for detuning effects caused by:

-   -   extraneous objects (metallic objects at LF and metallic and        dielectric objects at HF)    -   detuned power receivers in close proximity, and/or    -   variation of source impedances.

Tuning may also compensate for component tolerances, ageing, etc.

In one embodiment, tuning is automatically executed by the transmitter'scontrol system according to a defined procedure. A fractional tuningrange in the order of +/−10% may be desirable and also sufficient inmost scenarios.

Tuning can be capacitive or inductive or both.

Capacitive tuning may be accomplished by using mechanically tuneablecapacitors, e.g, driven by mini-motor/actuator. It can use electricallytuneable capacitors which tune using dielectric permittivity tuning orusing voltage-dependent capacitance such as varactor diodes. It can be aCapacitor bank and electronic or mechanical switches such as RF relays.

Varactor diode tuning may be limited at high voltages, and maydeteriorate the antenna Q-factor and cause harmonics.

Inductive tuning at LF may be accomplished through tapping the antennacoil and using mechanical or electronic switches as tap selectors. Atuneable inductor using a movable Ferrite core driven bymini-motor/actuator or permeability tuning using DC current biasing maybe used for fine tuning.

Another embodiment of fine tuning may introduce a second loop/Coil andalter the coupling factor to the main loop/coil by shape or orientation,using the so-called Variometer principle.

Another embodiment may change the coupling between the ferrite core andthe inductor electronically, or some other way, without physicallymoving the inductor relative to the ferrite core. While physicalmovement may be one way of changing the coupling, magnetic fields, orsome other way of adjusting the coupling can be used.

Electronically emulated reactance tuning may also be used. This emulatesa positive and negative reactance, thus decreasing and increasing aresonant frequency of a tank circuit.

In certain applications, it may be desirable to control orientation ofthe transmit loop to maximize energy transfer to a receiver that isarbitrarily positioned or oriented. The orientation control 170 canchange the physical or simulated orientation of the transmission.Alternatively, two or three magnetic field components with orthogonalpolarization may be generated. The sum field vector rotates, preventingfrom reception minima at any receiver orientation and position.

The control system 160 handles all of:

-   -   antenna tuning control    -   power and efficiency control    -   frequency generation    -   other housekeeping functions (e.g. system calibration, etc.)    -   radiation exposure control

In many applications, the position and orientation (coupling factor) ofreceiver(s) may change. The system can then adapt to the differentscenarios in order to satisfy power demand(s) of each receiver and tomaximize overall system efficiency. In a single receiver system, bothtransmitter and receiver may adapt independently, converging in maximumtransfer efficiency. One embodiment can operate without feedbacksignalling from the receiver to optimally adjust the transmitterparameters. The transmitter control system may simulate using localmodels of the LC circuit and may also simulate or estimate values of thereceiver circuit. The transmitter control system may determine the modelparameters using specific measurements such as antenna current andvoltage, input power, and calibration routines. The model may be used tooptimize transfer efficiency and/or to satisfy some minimum power demandof the receiver. For example, by sensing the current flow in thetransmit antenna, the model can determine information about the receivesystem.

The multiple receiver scenario imposes a more complex system. Onesolution can include feedback signalling from receivers.

The system can also control the radiation exposure. For example, thesystem can control reducing the transmitted power when persons areapproaching the transmit antenna.

A wireless interface 170 may be provided, e.g, for:

-   -   Device detection, identification, authentication, or    -   Communications/signalling between power transmitter and power        receiver (device)

Detection, identification and authentication of an energy receivingdevice may be used as analogs to remote sensing systems such as RFIDsystems. The communication can be bi-directional or unidirectional.

Data communications/signalling between energy source and energy sink mayuse the power carrier as a communication carrier. Higher Q factorchannels will have only limited bandwidth available, which will in turnlimit modulation index and/or transmission speed.

Another signaling alternative may use wireless communication such asBluetooth, Zigbee, etc. operating in other bands. Many portable devicesalready support such wireless interfaces for use for their owncommunication. In another embodiment, these interfaces are used by theenergy transfer system for feedback, in addition to their use forcommunication by the portable device.

The receiver is shown generically in FIG. 2 and includes similar partsto those of the transmitter of FIG. 1, in essentially reverse order.Specifically, the receiver includes a resonant antenna 210, tuning 220,matching 240, rectifier 250, load 260, control system 270, and wirelessinterface 230. Each of these subsystems are described in detail herein.

In a magnetically/inductively coupled system, the antenna 210 isgenerally a multi-turn loop of wire. At LF the magnetic antenna mayinclude a ferromagnetic or ferrimagnetic core e.g. a Ferrite rodantenna. At higher frequencies (HF) multi-turn loops may be used. Theantenna coil should withstand the high voltages and currents resultingwhen the receiver subsystem is operated at a highest loaded Q or inclose proximity of a transmitter. The Q-factor sets the transferefficiency, and higher Q factors improve the distance over which thepower can be received. Eddy currents and dielectric losses in thesurrounding of a receive antenna will deteriorate its Q-factor. This isparticularly true if the antenna is integrated into a device.

Q-factors up to 150 may be typical at LF and up to 200 in the HFfrequency range (13.6 MHz). In non-integrated laboratory samples,Q-factors twice as high may be achievable.

Similar materials can be used as described above.

At LF, the antenna coil may provide taps for matching or tuningpurposes. At HF, the use of a special coupling loop/Coil may be used tomatch to the impedance of the antenna.

Assuming a fixed operating frequency defined by the energy transmitter,tuning of the antenna's resonance frequency may compensate for detuningeffects caused by

-   -   extraneous objects (metallic objects at LF and metallic and        dielectric objects at HF)    -   detuned power receivers in close proximity    -   variation of load impedance

Tuning may also compensate for component tolerances, aging, etc.

Tuning can be automatically executed by the receiver's control systemaccording to a defined procedure.

A fractional tuning range in the order of +/−10% may be desirable andalso sufficient in most scenarios.

The resonant antenna can be changed by varying by anti-reactance(capacitance), or reactance of the inductive part of the antenna system.

Capacitive tuning may be accomplished by

-   -   mechanically tuneable capacitors (driven by mini-motor/actuator)    -   electrically tuneable capacitors (dielectric permittivity        tuning) or by    -   Capacitor bank (library) and electronic or mechanical switches        (RF relays)

Inductive tuning can also be used as above, e.g, by tapping the antennacoil and using mechanical or electronic switches (tap selectors). Atuneable inductor using movable Ferrite core driven bymini-motor/actuator or permeability tuning using DC current biasing maybe used for fine tuning.

Electronically emulated reactance tuning may also be used as above.

Matching can also be used as above.

In high coupling factor conditions, the rectifier/load may be insertedinto the series tank circuit in a similar way to the transmitter.However, in low coupling factor conditions the optimum load resistancethat maximizes the power into the load approaches the resonanceresistance of the receiver's tank circuit. This value might be as low asa few Ohms, depending on the tank circuit's L/C ratio. A specialmatching using either a special coupling loop and/or a tapped antennacoil, and/or a capacitive voltage divider may be used to transform theimpedance imposed by the rectifier/load.

The rectifier 250 converts the AC power induced into the receiverantenna into DC power. The rectifier uses current rectifying electroniccomponents such as diodes with low threshold voltage or electroniccircuitry such as transistors that switch synchronously to the receivedAC.

The rectifier should dissipate as small an amount of power as possible.Therefore, appropriate antenna matching configuration, and loadimpedance adaptation may be used, especially if simple diode rectifiersare used.

Synchronous rectification may be more complex but provides the potentialof low power dissipation, particularly at low rectifier input voltages,the low impedance case.

The load includes

-   -   the target load that consumes the transferred energy (e.g.        battery of a device, device circuitry)    -   load imposed by the energy receivers own supply (control        functions)    -   load impedance adaptation and load power control, e.g., using a        DC/DC converter, ideally with minimum power losses. Depending on        the load characteristics, this can act as a step-down or a        step-up converter.

The control system 260 of the receiver carries out:

-   -   antenna tuning control    -   power and efficiency control    -   Frequency generation, e.g. if the load requires other than the        60 Hz power frequency, and    -   other housekeeping functions such as system calibration.

In many applications, the receiver's position and orientation (couplingfactor) may change. There may be advantages in having the receiverautomatically adapt to the different conditions in order to control andmaintain power into the load at a desired level and to maximize receiverefficiency.

In a single receiver system, the receiver may adapt independently fromthe transmitter, e.g., using a model as described above, that determinesmodel parameters using specific measurements (e.g. antenna current andvoltage, input power, etc.) and calibration routines. Based on thislocal model, the receiver's parameters may be optimized to maximizetransfer efficiency and to satisfy the power demand of the receiver. Ifthere are multiple receivers, then the model technique above can beused, or the energy receiver and/or transmitter can could feed back datato the other.

Moreover, the system may carry out radiation exposure control e.g. byreducing its power when persons are approaching the parasitic antenna.As in the transmitter case, the wireless interface 270 may be omitted,or can be used for device detection, identification, authentication, orcommunications/signalling between power transmitter and power receiver.

Detection, identification and authentication of an energy receivingdevice may be used like current RFID systems, using any of the currentRFID standards. Any of the techniques described for the transmitter maybe used, including using the power carrier as the communication carrier,or using wireless standards such as Bluetooth, Zigbee, etc. operating inother ISM-bands.

FIG. 3 illustrates an energy relay system, that uses a parasitic antennato repeat wireless power in an area.

The generic wireless energy relay uses a resonant parasitic antenna 310that is resonant with the frequency being repeated. A tuning circuit 320can be formed of a capacitor and inductor. The system uses matching 330,a rectifier 340, and optionally a load. A control system 350 controlsthe operation. This energy relay may be used to extend coverage/range ofa wireless energy transfer system. It receives energy from an energytransmitter and relays it to an energy receiver. The energy relay may bealso considered as a parasitic antenna that locally amplifies the fieldstrength.

In a magnetically/inductively coupled system, the antenna 310 isgenerally a multi-turn loop (coil) in series with a capacitor. At higherfrequencies (HF) single turn loops may be used. The antenna coil must beable to withstand the high voltages and currents resulting when theenergy relay subsystem is unloaded (no receivers within range) and/orwhen the relay is close to the energy transmitter. It must provide aQ-factor as high as possible since this Q-factor will limit transferefficiency at the fringe of the extended service coverage and range.

Q-factors up to 300 are achievable at LF and up to 600 in the HFfrequency range (13.6 MHz). In non-integrated laboratory samples, theQ-factors may be doubled. The materials and components needed to build aparasitic antenna may be the same or similar to those used in an energytransmitter. The parasitic antenna 310 may be tuned in a similar way tothose discussed above.

In a similar way, the matching 330 may use the techniques describedabove.

Rectifier 340 is used to extract DC power that is locally consumed,e.g., by the control system and other circuits. This may use similarstructure to that described above. The control system 350 can be usedfor antenna tuning control and/or for power and efficiency control. Insome applications the relay's position and orientation (coupling factor)may change. This may indicate that the relay should automatically adaptto the different conditions.

In an embodiment, the relay may adapt independently from the energytransmitter, using any of the techniques described above.

A wireless interface may also be used, as described above, to detect,identify, and authenticate an energy relay, to activate and deactivatean energy relay and/or to transmit information about the operationalstatus of an energy relay

The wireless power system can be used to provide an entirely wirelessdesktop IT environment as shown in FIG. 4. Handheld communicationsterminals and IT peripheral devices are powered or recharged from acentral power source via a wireless energy transfer. A preferredtechnique for wireless energy transfer is based on coupled magneticresonance using magnetic field antennas, e.g., a loop or coil operatingeither in the LF or HF frequency range.

FIG. 4 shows the wireless desktop embodiment using a personal computerwith a screen 400. The screen 400 has a base 402 with an antenna 404embedded therein. The base may be disk-shaped and may embed a circularwire loop antenna to generate a substantially vertically polarizedmagnetic field.

Wireless power enabled devices can be placed on a desktop and mayreceive power from the power transmitter unit. The power transmitterunit as well as the display 400 is operated from AC power, e.g., 110VAC. This can be used to power desktop devices such as keyboard 410,with its internal antenna 412, mouse 420 with antenna 422, and otherpersonal electronic devices such as mobile phones, music players, PDAs,etc. The placement of these items on the desktop creates apreferentially coplanar orientation of their internal antennas e.g 412,422 to the transmit loop antenna 404.

For other devices such as cordless phones, digicams, etc. that areusually placed on a recharging station, the wireless power receiver andits antenna may be integral parts of the recharging station such as 430.

Power receiving devices providing enough space to integrate moreeffective antennas may also serve as power relays for other low powerdevices placed close to those devices, as shown in FIG. 5.

Other embodiments may be used for variants of a wireless powering orcharging station for low power portable electronic devices. An exampleof a wireless powering or charging station with a portable electronicdevice (e.g. a cordless phone) is shown in FIGS. 6 and 7. Thisembodiment may embed a parasitic antenna into a charging base thatrelays the wireless power to an internal antenna 705 in the portabledevice 710. In this embodiment, the internal antenna 705 is a ferriterod antenna. Since the device 710 and its internal antenna 705 ismaintained in a specified location relative to the parasitic antenna700, the relay of power can be tuned to an exact location, and the powertransfer can hence be very efficient.

An embodiment uses magnetically coupled resonance to transfer the powerfrom source to receiver. In contrast to ordinary inductive coupling,loosely coupled resonant loop/coil antennas, preferentially of highquality factor, are used for energy transfer. The operating frequency ispreferably either in the LF or HF frequency range.

In variant 1, depicted in FIG. 7, both the wireless charging station 699and the portable device 720 integrate a resonant magnetic antenna. Thecharging station 699 preferably accommodates a loop/coil antenna 700making efficient use of the space in the socket of the station, whilethe portable device uses an integrated Ferrite rod antenna or anotherloop/coil structure with suitable form factor. The wireless chargingstation antenna 700 is a secondary antenna that receives electricalenergy from a power base station primary antenna such as 800. This isthen relayed to the antenna 705 of the portable device 710 which is thetertiary antenna 705. This principle is illustrated in FIG. 8.

The portable device 710 may also receive energy directly from the powerbase station 800. The antenna 705 integrated in the portable device 710may be less efficient than the antenna 700 integrated in the chargingstation. As the distance between the primary antenna 800 and thesecondary antenna 700 increases, less power can be received directly.The secondary antenna in essence locally magnifies the magnetic field inthe vicinity of the charging station increasing the overall efficiencyof the receive antenna in the portable device. Therefore, thisembodiment can be used to increase the distance of wireless powering andcharging; however, when the unit is placed closely enough to the primaryantenna, the portable device may also receive electrical energy directlyfrom the power base station, thus not requiring a special chargingstation. Moreover, the magnetic coupling between charging station andportable device may have special advantages—as discussed above, it canavoid soiling, and oxidation and can be used for multiple differentdesigns of portable devices.

Another embodiment is shown in FIG. 9. In this embodiment, electricalenergy received by the wireless charging station is forwarded to theportable device using conductive coupling over contacts 900, 902.

Another embodiment shown in FIG. 10 receives power through a wiredconnection e.g. directly from the 110/230 V AC source over wire 1010.However, power is forwarded to the portable device based on magneticcoupled resonance between transmit antenna 1020 and receive antenna1030.

Another application for wireless power is a wireless power bridge, thatrecognizes that in certain circumstances, it may be convenient totransmit power through walls or windows.

A first embodiment may use this device to power a laptop PC or otherbattery operated device with limited autonomy on a terrace or balconywhere there is no AC socket. Mounting an AC socket might not beconvenient, and the only alternative is an extension cord. In thisexample, a wireless solution can facilitate transfer of power throughwalls or windows may be used. The indoor component of this wirelesspower transfer system can be left permanently installed and the outdoorcomponent is a lightweight accessory or a laptop PC that can be easilycarried in a transport bag.

Another embodiment uses this system for powering of sensors mounted tothe exterior wall of a house (e.g. burglar alarm system), where it couldbe otherwise difficult to power those devices.

A Wireless Power Bridge may provide a standard AC socket or a DC poweroutlet (e.g. 12 VDC). These two variants of a Wireless Power Bridge aresketched in FIG. 11 and FIG. 12, respectively. The transmit subsystemmay also produce an invisible local power hot spot that enables easyaccess to electric power from the other side of a wall using acompatible receiving device.

The Wireless Power Bridge is based on magnetic-field inductive couplingbetween a resonant transmit antenna and a resonant receive antenna. Thisuses a non-modulated carrier frequency, of, for example, 50 Hz, that isappropriate for wireless transmission through a wall or window. Thepreferred frequency is in the range from 20 kHz to 135 kHz (VLF, LF).Another embodiment directly uses the AC power frequency, typically 60Hz, for wireless energy transfer. One embodiment efficiently transferspower through a non-metallic wall of thickness in the range of a few mmup to 40 centimeters also depending on the size of the antenna. This isaccomplished through use of two resonant antennas applying coupledresonance with a high Q-factor (typically >200).

Depending on the dimensioning of the system and the separation of thetransmit and receiver antenna (transmission distance) the system may becapable of transferring power up to 100 W, or similar. This can be usedto supply e.g. a laptop computer or other devices with similar powerconsumption.

The system is generally composed of the following components:

-   -   Power cord to connect to standard AC socket (e.g. 110 VAC/60 Hz        or 220 VAC/50 Hz).    -   Transmit power converter unit that converts supply AC voltage        and frequency (e.g. 110 VAC/60 Hz or 220 VAC/50 Hz) into another        voltage and into another frequency (typically >50 Hz) that may        be more appropriate for wireless transmission through a wall or        window. In one embodiment, the transmit power converter unit        uses the standard 60 Hz frequency as the power transmission.    -   Transmit antenna unit (flat panel) that is resonant on the        operating frequency.    -   Receive antenna unit (flat panel) that integrates a multi-turn        loop (coil) and a capacitor to achieve resonance at the desired        operating frequency.    -   A receive power converter unit that integrates an AC/DC or AC/AC        frequency converter, which reconverts the frequency used for        wireless transmission into the required DC voltage or a standard        AC supply voltage and frequency.

FIG. 11 shows an arrangement to transmit power through a wall andthrough a window. The distance between the transmit and receive antennacan vary, thus varying the coupling factor. In one embodiment, thesystem automatically adapts to the actual conditions in order to meetpower requirements at receive side and to maximize transfer efficiency.

Moreover, the system may provide automatic antenna tuning to compensatefor detuning effects caused by the environment or component tolerances.

The transmit and receive antenna can be coaxially aligned to obtainmaximum transfer efficiency. An indicator (e.g. a lower power LED) builtinto the receive power converter unit may be used, where the LED isbrighter as the coupling improves. This technique can be used to findthe optimum position of the receive antenna yielding maximum transferefficiency.

FIG. 13 shows a block diagram of a transmit subsystem that can be usedwith any of the wireless power embodiments described in thisapplication. The subsystem includes transmit power converter unit 1300,and transmit antenna unit 1310.

The transmit power converter unit 1300 has a number of subunits. Arectifier & filter assembly 1320 generates the raw DC voltage used bythe following stages. This can be used by a DC/DC converter 1330providing the power that is eventually fed to the transmit antenna unit1310. An auxiliary DC/DC converter 1340 can be used to supply thefrequency generation and control subunit with power. A tuning network1350 can also be powered, in order to maintain precise resonancemaximizing antenna current. An antenna current sense 1360 can similarlymeasure antenna current in terms of magnitude and phase based on powerfrom the converter.

A frequency generation and control subunit 1370 carries out manydifferent functions, including:

-   -   generating the frequency used for wireless power transmission,        driving the power stage, e.g. the half bridge inverter 1380,    -   automatically controlling functions of the transmit subsystem,        as described herein, to control power and efficiency of the        Wireless Power Bridge.    -   control human interface for manual control of the transmit        subsystem. this can include, for example,        activation/deactivation, power control, etc.

A Wireless Power Bridge can be configured to transfer power up to 100 Wand can use a transmit power converter unit with a form factor and outerappearance similar to that of an external power supply used to supplye.g. a laptop computer or other similar power device.

The rectifier & filter subunit 1320 may include functions that arecontrolled by the frequency generation and control subunit over controlinterface A. Typically, the DC/DC converter 1330 is a step-downconverter providing an output DC voltage that is lower than its inputvoltage. In general, the output voltage generated by the DC/DC converter1330 is variable and controlled by the frequency generation and controlsubunit via control interface B for power control and to achieve maximumenergy transfer efficiency.

In one embodiment, this DC/DC converter may be omitted, in which casethe power stage (half bridge inverter) is directly supplied by therectifier and filter subunit. In one embodiment, a switching powersupply can be used.

The auxiliary DC/DC converter subunit 1340 provides a fixed DC outputvoltage to supply the frequency generation and control subunit 1370, aswell as the other powered units.

The power stage generating the power carrier used for wireless powertransmission is preferably a half bridge inverter 1380 using twoelectronic power switches, e.g., FETs or transistors, in a ‘push-pull’configuration. The power stage is driven and controlled by the frequencygeneration and control subunit via the control interface B. Power andtransfer efficiency control is accomplished through modifying the DCsupply voltage of the power stage, and the duty cycle/pulse width of theswitching waveform as generated by the frequency generation and controlsubunit.

In one embodiment where the DC/DC converter provides a fixed DC outputvoltage, power and transfer efficiency is solely controlled by the dutycycle of the switching waveform.

In another embodiment where the standard AC supply frequency is directlyused for wireless power transmission, the power stage is formed of aphase controlled modulator controlled by the frequency generation andcontrol subunit.

The tuning network 1350 can be used to adjust parameters to maintain theantenna operated at resonance. In one embodiment, a fixed and crystalstabilized transmission frequency may be used. This may assist withfrequency regulatory issues to reduce the risk of harmfulelectromagnetic interference to other systems.

This is particularly true for all applications requiring maximumtransmission range and efficiency, thus operated with high ‘loadedQ-factor’.

The tuning network may also compensate for possible detuning effectscaused by the receive subsystem and/or extraneous objects in proximityof the transmit antenna, as well as by the reactive components in thesource impedance of the power stage.

The tuning network can also compensate for tolerances (ageing) ofcomponents of the transmit antenna unit and its feeder cable.

The tuning network may also be controlled by the frequency generationand control subunit via the control interface C.

Certain embodiments may only require a limited transmission range (e.g.high coupling factor between transmit and receive antenna). In thatcase, the tuning network may not be needed.

The antenna current sense is used by the frequency generation andcontrol subunit to measure the antenna current in terms of magnitude andphase (sense interface D). The current sense should be done in a waythat will not deteriorate the Q-factor of the antenna system. In oneembodiment, voltage sensors on receiving devices are used that feed thereceive information to the transmitters. An adaptive power transmitterramps up power in steps and senses the stimulated power levels.

The frequency generation and control subunit generates the frequency andthe switching waveforms that to drive a half bridge inverter forming thepower stage. The subunit also measures the transmit antenna currentusing the antenna current sense and adjusts operational parameters ofthe transmit power converter to satisfy power demand by the receiver(within specified limits). In this way, the power converter can achievemaximum energy transfer efficiency. In one embodiment, the maximumoperation may be carried out according to the techniques described inour co-pending application Ser. No. 12/394,033, filed Feb. 26, 2009, theentire contents of the disclosure of which is herewith incorporated byreference.

In one embodiment, the frequency generation and control subunit does notcommunicate with other entities of the receive subsystem. Bothsubsystems act independently to determine how to satisfy power demand bythe external load connected to the receive subsystem to optimizeoperating parameters on both the transmit and receive side in a mannerto converge at maximum energy transfer efficiency.

The frequency and control subunit 1370 may also include a user interfacefor activating/deactivating the transmit power converter unit and tomanually modify parameters.

The transmit antenna unit 1310 is a purely passive device, fed by thetransmit power converter unit via the antenna feeder cable 1309. Thecable 1309 can be of length typically 1 m, and may be of a quality andhave voltage ratings similar to that of a standard double wire AC cable.

The transmit antenna unit includes a multi-turn loop (coil) and a highvoltage capacitor forming a principal part of a series tank circuit. Themulti-turn loop is made of well insulated copper wire, set to withstandthe antenna voltage that may occur in the worst case. In a typicaldesign, the r.m.s. voltage may be above 1000 V depending on the systemsactual power rating and the specified maximum transmission distance.

Assuming an operating frequency in the range between 20 kHz and 135 kHz,preferably an adequately stranded wire such as Litz wire may be used toreduce eddy current losses from skin and proximity effects and tomaximize unloaded Q-factor.

In a typical design, the capacitor should be sized to withstand r.m.s.voltages >1000 V depending on the system's actual power rating, thecircuit's actual Q factor, and the specified maximum transmissiondistance.

A typical layout of a flat panel transmit antenna unit is shown in FIG.14. The antenna 1400 is formed of a coil part 1405 and a high voltagecapacitor 1410. The high voltage capacitor 1410 is mounted in theinterior of the loop to save space and to provide a maximum loop sizefor a given outer contour form factor. Since the HV capacitor isintegrated into the antenna unit, high voltages resulting from resonancewith a high Q-factor (high loaded Q) are kept in its interior and do notappear either on the feeder cable nor in the transmit power converterunit. This thus simplifies design and relaxing certain requirements.

The transmit antenna unit 100 may provide special fixtures that simplifypermanent mounting or temporarily suspending of the flat panel antennato walls or windows. FIG. 14 shows suction cups 1420 and suspendinghandles 1422.

The receive subsystem is shown in FIG. 15. As in the transmit subsystem,the receive subsystem is formed of a receive antenna unit, and a receivepower converter unit 1510. Many of these units are very similar to thosediscussed above.

The receive antenna unit 1500 may be identical to the transmit antennaunit 1310. In another embodiment, the dimensioning of the receiveantenna may be different with respect to form factor, constitution, andelectrical characteristics, in order to fit this device.

The receive antenna unit feeds the receive power converter unit via theantenna feeder cable 1501, similar to the cable 1309.

The receive power converter unit 1510 may include any or all of anantenna current sense 1520, a tuning and matching network 1530 tomaintain precise resonance of the receive antenna by maximizing antennacurrent and to match the rectifier to the receive antenna, a rectifier1540 generating the raw DC voltage required by the following stages.

A DC/DC or DC/AC converter 1550 may be used to generate a DC or standardAC supply output, respectively, with a voltage and current satisfyingthe requirements of the external load 1599 connected to the receivesubsystem. It may also include an auxiliary DC/DC converter 1555 tosupply the frequency generation and control subunit and other powerconsuming units.

A voltage sense 1560, and current sense 1565 may be used to measureoutput voltage and output current into the external load 1599.

As in the transmit unit, there is a frequency generation and controlsubunit 1570 that automatically controls all relevant functions andparameters of the transmit subsystem to control power and efficiency ofthe Wireless Power Bridge. This may also include, for example, a userinterface that controls manual control and modification of settings viahuman interface. This can include activation/deactivation, power,voltage and current rating, etc.

The unit 1570 can also generate the standard AC supply frequency asspecified for the external load.

Assuming a Wireless Power Bridge dimensioned to transfer power up to 100W, the receive power converter unit might typically have a form factorand outer appearance similar to that of an external power supply used tosupply e.g. a laptop computer or other appliances of similar powerrating.

The antenna current sense is used by the frequency generation andcontrol subunit to measure the receive antenna current via senseinterface D. The current sense preferably should not deteriorate theQ-factor of the antenna system.

The tuning and matching network is generally used to ensure that thereceive antenna is operated at resonance and that the rectifier's inputimpedance is optimally matched to the receive antenna. This isparticularly true for all applications requiring maximum transmissionrange and efficiency.

The tuning and matching network compensates, as above, for possibledetuning effects caused by the transmit subsystem and/or extraneousobjects in proximity of the receive antenna, and by the rectifier's loadimpedance. It compensates for tolerances (aging) of components of thereceive antenna unit and its feeder cable.

The tuning and matching network is controlled and may also bereconfigured by the frequency generation and control subunit via thecontrol interface C.

One embodiment of the Wireless Power Bridge requires only limitedtransmission range, such as would be the case for high coupling factorbetween transmit and receive antenna. In this case, the tuning andmatching network may be omitted.

The Rectifier rectifies and filters the AC voltage as induced into thereceive antenna providing the raw DC feed to the following stages. Therectifier and filter subunit may include functions that are controlledby the frequency generation and control subunit via control interface A,as above.

The DC/DC or DC/AC converter may be a step-down or step-up converterdepending on the application, providing an output voltage and currentsatisfying the requirements of the external load connected to thereceive subsystem. In general, the output voltage or current generatedby the DC/DC or DC/AC converter is variable and controlled by thefrequency generation and control subunit via control interface B. in oneembodiment, this converter may be omitted, and the external load is thenfed directly by the rectifier.

In an embodiment where the standard AC mains frequency is directly usedfor wireless power transmission, the DC/DC or DC/AC converter may bereplaced e.g. by a phased controlled modulator controlling outputvoltage and current into the external load.

The auxiliary DC/DC converter subunit provides a fixed DC output voltageto supply the frequency generation and control subunit.

The frequency generation and control subunit automatically controls allrelevant functions and parameters of the receive subsystem to satisfyvoltage and current requirements of the external load and to maximizeenergy transfer efficiency. If needed, it generates the standard ACfrequency as required by the external load and feeds this frequency tothe DC/AC converter subunit via control interface A.

Additionally, this measures the antenna current by means of the antennacurrent sense, the DC or AC output voltage and current by means of thevoltage and current sense, respectively. These measurements may be usedto compute and/or adjust relevant operational parameters andconfigurations of the receive power converter unit in order to satisfypower demand by the receiver (within specified limits) and to maximizeenergy transfer efficiency.

The receive subsystems act independently from the transmit subsystem tosatisfy requirements by the external load, while optimizing the receiveoperating parameters to maximize transfer efficiency.

The frequency and control subunit may also provide a human interface foractivating/deactivating the receive power converter unit and to manuallymodify parameters or configurations.

Efficient wireless energy transfer based on magnetic coupled resonancemay be more efficient when using resonant antenna circuits with highestpossible quality factor in both energy transmitter and energy receiver.

High Q-factor in conjunction with energy transfer in the order ofseveral watts means high reactive power in the LC tank circuit, sincethe Q factor can be expressed as:

$\begin{matrix}\frac{P_{reactive}}{P_{real}} & {{Equation}\mspace{14mu} 5\text{-}1}\end{matrix}$

High reactive power means high AC voltages/currents across/through theantenna inductor and its anti-reactor/capacitor.

The antenna can have different designs depending on the application. AtLF, the typical solution may be a multi-turn wire loop or coil. A high Qcoil can be obtained in one of different ways. One way is to use thincopper wire and a large number of turns for the coil. Another approachmay be to use thicker appropriately stranded wire (Litz wire) with alower number of turns. The Litz wire is formed of individually insulatedstrands with an optimum diameter for the operating frequency. Anotherway is to use an appropriate ferrite core and Litz wire with a lownumber of turns.

The thin/larger number of turns technique may provide a high impedancecoil. This means a high reactance and relatively high loss seriesresistance. This is Q-times lower than the magnitude of the coil'sreactance, where Q refers to the Q-factor of the coil that may normallybe assumed as the overall Q-factor of the tank circuit.

The Litz wire approach 2 may result in a solution with a lower impedancecoil. This means a lower reactance and relatively low loss seriesresistance, e.g., Q-times lower than the magnitude of the coil'sreactance.

The ferrite approach could produce high magnetic field strength(saturation) and resulting low coil Q-factor due to hysteresis losses inthe core material.

Assuming equal Q, the thin wire/large number of turns approach mayprovide a higher voltage at resonance. This in turn provides a higherrisk for arcing/discharge particularly with respect to the thinner wireused. Litz wire may provide a solution with higher power transfercapability. On the other hand, if too low impedance is targeted, it maybecome more difficult to find a capacitor with low enough equivalentseries resistance and that can support the high current, particularlyunder space constraints.

The antenna must also be matched to the power stage. A relatively simpleand stabile transmitter solution is obtained by using a low impedanceoutput power stage formed of a voltage source with a half-bridgeinverter and a series tank circuit. High efficiency would require thistank circuit to have a series resonance resistance that is higher thanthe source resistance of the power stage.

For HF (e.g. at 13.6 MHz), similar considerations can be made resultingin similar conclusions. However the number of turns needed willgenerally be lower at HF, and instead, much thicker wire and larger wirespacing will be required to mitigate skin and proximity effects. Litzwire optimized for frequencies above 1 MHz is not commercially availableand probably less useful due to other design constraints.

Another effect often overlooked degrading Q-factor is energy absorptionin lossy materials in the antenna's surrounding. The magnetic andelectric fields generated by the antenna can cause eddy current lossesin non-perfectly conducting materials, magnetic polarization hysteresislosses in magnetic materials and electric polarization losses indielectric materials

At LF, dielectric losses are normally negligible. Q-factor degradationis mainly due to eddy currents and hysteresis losses in conducting andmagnetic materials, respectively.

At HF, eddy currents and dielectric losses are mainly responsible forQ-factor degradation.

In many applications of wireless power, the surrounding area of amagnetic antenna is dominated by dielectric materials. In such anenvironment, low impedance antennas that generate higher currents(magnetic fields) but lower voltages (electric fields) generally performbetter.

This aspect of Q degradation is of particular importance, if an antennamust be integrated into a device (e.g. into a foot of a PC screen).

Summarizing, the following aspects maybe considered when designing ahigh Q transmit antenna:

To obtain maximum inductance at lowest resistance (highest Q-factor) thewinding should be as dense as possible, meaning that the cross sectionalarea of the winding must be as low as possible. This is howevercontradictory to skin and proximity effects and volume needed for wireinsulation that must sustain the high resulting voltages, and for powerdissipation, e.g, for copper losses.

Above considerations show that practical designs require thoroughanalysis, complicated tradeoffs and optimizations taking into accountall design constraints affecting efficiency of a transmit antenna(volume, form factor, cost, power rating, characteristics andavailability of passive and active electronic components, as well asintegration aspects).

In most wireless power applications, the size of the energy receiversare constrained to small devices. Furthermore, extra cost needed forenabling wireless power in an electronic device ideally should notsignificantly increase overall manufacturing costs. The power to behandled in a receiver of a small device will typically not exceed 1-2watts.

At LF, a loop shaped coil either made of very thin well insulated wireor appropriate Litz wire may be used. However, the effective loop areapredominantly affects the performance of the energy receiver. Thereforean effective loop area as large as possible should be obtained. Themulti-turn loop ideally should fully encompass the perimeter of thedevice.

Severe Q-degradation due to eddy current losses in all conducting partsof the device might be expected, however, since the entire electronicsis in the interior of the loop, where the magnetic field is highest.Many reasons exist to avoid a metallic housing for this system. The highmagnetic field strength may also require special measures to avoidinterference into the electronics.

Loop antennas that can be folded out would be preferable in someembodiments. However, the increased mechanical complexity andmanufacturing costs of a device may limit its application.

Ferrite antennas and other magnetically permeable materials may beparticularly interesting, since they artificially increase the effectivearea of the coil and additionally concentrate the magnetic field linesinto the Ferrite core. Q-factors up to 100 may be achieved withappropriate Ferrite materials at 135 kHz and for a power of 1 W.However, to achieve an effective area comparable to wire structuresencompassing the device largest perimeter, Ferrite rod antennas must berelatively long thus becoming bulky and also heavy.

Combinations of the above approaches may also be used. For example, anantenna can use a flat disk-shaped multi-turn loop on a Ferrite backing.This Ferrite substrate might be a few mm thick. Ferrite backing,however, may compromise the effective area of the antenna.

Efficient wireless energy transfer based on magnetic coupled resonanceuses resonant antenna circuits with high quality factor in both energytransmitter and energy receiver.

High Q-factor means low bandwidth thus little tolerance for variationsof L and C values due to manufacturing tolerances, aging, environmentaleffects (temperature, extraneous objects interacting with the magneticor electric field surrounding the LC circuit, non-linear and memoryeffects, e.g. in conjunction with the use of permeable magneticmaterials.

Therefore in practical high-Q designs readjusting tuning of theresonance frequency may help keep a high Q. A resonant antenna systemthat is automatically tunable can use tunable capacitor(s) and/ortunable inductances, e.g, electrically tuneable reactors. Both must becapable of withstand either high voltages or high currents and made ofmaterials that do not impair the antenna's Q-factor.

The capacitive tuning can use a set of capacitors, e.g., a capacitorbank, in a series or parallel arrangement with RF switches that may beopened or closed to adjust the effective capacitance. This method isparticularly useful at LF where mechanically variable capacitors becomemore bulky.

FIG. 16 shows an embodiment of a series resonant transmitter circuitwith a tuning capacitor bank 1600 in a parallel arrangement but inseries to the principal capacitor 1610. Relays or bipolar semiconductorssuch as FETs may be used as switching elements 1602 to add or remove theindividual capacitors 1604.

Higher Q circuits may require an increasing number of tuning capacitorsand tuning switches in the capacitor bank to provide a fine tuningcapability while maintaining the required tuning range. Further, as theQ of the LC tank circuit increases, the voltage supported by thecapacitor bank increases. The tuning capacitors and the tuning switchesare preferably rated for higher voltages. Moreover, because thecapacitor bank is in series with the antenna circuit, the tuningcapacitors and tuning switches must support high currents and relativelyhigh voltages depending on the tuning range.

The capacitor bank tuning may be combined with a continuously tuneablereactance 1620 for fine tuning.

At HF, tuning maybe realized with a tuning capacitor of small value inparallel to the principal capacitor as shown in FIG. 17. An embodimentmay use a mechanically variable capacitor 1702 driven by a mini-actuator1704.

An alternative to capacitance tuning at HF and LF is using a variableinductor as shown in FIG. 18. This may be accomplished by

-   -   a tapped antenna coil and electromechanical or electronic        switches forming a tap selector,    -   a mechanically adjustable ferrite core driven by a        mini-actuator,    -   permeability tuning of a ferrite core using a DC bias current        Permittivity tuning of a capacitor using a DC bias voltage,        which may be considered as the physical dualism to permeability        tuning, may also be an option for both HF and LF.

Another approach to fine tuning is to introduce a second loop/coil andaltering the coupling factor to the main loop/coil by changing its shapeor orientation using the variometer principle.

FIG. 19 illustrates a further method that maybe considered for finetuning e.g. in conjunction with a capacitor bank for coarse tuning. Thispurely electronic method avoids any tuneable reactance components.Instead, it compensates for the antenna current drop in off-resonanceconditions by increasing the output voltage of the power stage (e.g.half bridge inverter).

The power stage may be considered as emulating the voltage resulting atthe output of a constant voltage source with a tuneable sourcereactance.

Relatively high output voltages may be required in order to provide auseful tuning range, thus setting more stringent requirements to theelectronic switching elements of the power stage if efficiency is to bepreserved.

The fine tuning control loop senses the antenna current and controls theoutput voltage such that the desired antenna current results.

The general principles, methods, considerations, and conclusionsdescribed relative to the transmit antennas also apply to the tuningproblem of a receive antenna. In receiver applications, however, spaceand cost constraints are typically much more stringent than intransmitters, particularly regarding integration into small portabledevices. On the other hand, relaxed requirements with respect to antennavoltages and currents can be expected since small receive antennas willtypically be rated for lower power, and provide lower Q-factor thantransmit antennas.

Capacitor bank tuning as typically used at LF may be less favorable withrespect to space constraints.

At HF, tuning maybe realized with a tuneable capacitor of smallcapacitance in parallel to the principal capacitor as in FIG. 17. Itsrealization may be a mechanically variable capacitor driven by amini-actuator.

A permittivity tuneable capacitor using a DC bias voltage may be usedfor LF and HF.

An embodiment may use a variable inductor of the type shown in FIG. 20.This may be use a tapped antenna coil 2000 with capacitor 2010.Electromechanical or electronic switches form a tap selector 2030 forcoarse tuning. A mechanically adjustable ferrite core 2040 is driven bya mini-actuator 2050.

Another embodiment may use permeability tuning of a ferrite core using aDC bias current for fine tuning.

Another embodiment shown in FIGS. 21A and 21B may alter the inductanceof the antenna using a mechanically movable coil 2100 that slides todifferent positions, driven by a mini-actuator 2105. The position of thecoil over the ferrite sets its inductance.

Mechanical tuning of a ferrite rod antenna has the advantage of notrequiring any additional components in the tank circuit thus maintainingthe Q-factor.

FIG. 22 illustrates a further method that may be used for fine tuning areceive antenna e.g. in conjunction with a capacitor bank for coarsetuning. This purely electronic method avoids any tuneable reactancecomponents. A switched-mode power conversion shown as 2200 creates anantenna load impedance that can be varied in terms of both resistive(real) part and its reactive (imaginary) part. The reactive part addsreactance into the series tank circuit, thus changing its resonancefrequency.

In the embodiments, a signal can be formed that is indicative of a needfor tuning, e.g., a signal indicative of mismatch, or power degradation,or inductance, or the like. This signal can be used to adjust thevariable capacitor or the variable inductor, or both.

Integration of receive antennas into small electronic devices is aparticular design challenge as there may be limited space available foradditional components. Also, the, small form factor limits antenna area,and hence limits the antenna performance. There are also dielectric andeddy current losses in PCBs and other components containing lossydielectric and metallic structure lowering antenna Q-factor. There isalso a potential of electromagnetic interference to certain devicefunctions.

Ideally, a high Q resonant loop/coil antenna should be separated fromthe device main body, e.g. in a part that can be folded out for thepurpose of wireless charging. A device/keyboard cover that can be foldedout and that integrates the wireless power antenna as shown in FIG. 22Amay be used in a clamshell style phone.

Another embodiment integrates the antenna into a part, causing lowerlosses and providing better penetration of magnetic fields because itcontains less metallic and/or dielectric structure, e.g. in the keyboardpart of a mobile phone (see FIG. 22B. This may be considered as the“compact” configuration.

At LF eddy currents induced into metallic structures may be thepredominant loss contributor. At HF, both eddy currents and dielectriclosses may degrade the Q-factor.

At LF, ferrite rod antennas are particularly interesting with respect totheir integration in small compact devices. Ferrite cores tend toconcentrate the magnetic field into the core, reducing magnetic fieldstrength in the surrounding thus lowering eddy current losses in thedevice.

FIGS. 22C and 22D show ferrite cores integrated into claim shell andcompact devices respectively. A ferrite rod antenna uses a magneticfield perpendicular to that of an air coil aiming at maximum induction.Thus orientation either of transmit antenna or device should be changedrelative to a system using a device with an integrated air loop receiveantenna.

Wireless energy transfer based on magnetic coupled resonance generallyinvolves a number of power conversion stages in both transmitting andreceiving subsystem. This can be seen e.g. from the block diagrams ofthe Wireless Power Bridge as shown in FIGS. 13 and 15. In order toachieve high end-to-end transfer efficiency, each stage should beoptimized, to prevent losses from accumulating across the chain. On thetransmit side, particular emphasis could be placed on the power stagedriving the transmit antenna. Typically, a half bridge inverter inconjunction with a series antenna tank circuit is used for wirelesspower transmission at LF. This is particularly advantageous since thiscircuit results in a maximum output current at resonance and a currentdrop in off resonance conditions and generally low harmonic levels.

High efficiency will be obtained when the real part of the inverter'ssource impedance is considerably smaller than the equivalent series lossresistance of the antenna tank circuit. Efficiency is also improved whenthere is little or no power dissipation in the transmitter's sourceresistance. All generated energy is either transferred to a receiver orpartially dissipated in the transmit antenna's loss resistance.

Power and efficiency control of the transmitter may be performed byeither the DC supply voltage of the half bridge inverter or by the dutycycle of the driving waveform, or both.

On the receive side, the rectifier and load adaptation may be important.A rectifier can be built with very low voltage drop and ohmic losses.The rectifier may be inserted directly into the antenna circuit e.g.into a series tank circuit, analogous to the transmitter. Efficiency isagain improved when the resistive losses in the rectifier are minimized.Classical rectifiers e.g. Schottky diodes might have too high a loss andhence so-called synchronous rectifiers based on synchronously switchedtransistors may be preferred.

Load adaptation and current control (in case of wireless batterycharging) may be performed with efficient step-down or step-upconverters.

In a multiple receiver scenario, adaptivity over a wide range may beuseful, so that these receivers can be able to maintain power into loadat any coupling factor and in a worst case without assistance of thetransmitter.

In a single receiver scenario where the distance between transmit andreceive antenna may vary over a wide range. Therefore, power transferinto the load at the receive end may be controlled. This will be true inmany wireless powering and charging applications.

Overall system efficiency is a wholly separate issue from receivedpower. A system that performs both power and efficiency control willhave the goal of converging to a state where overall transmissionefficiency is at a maximum. In this state, receive antenna will bedifferently loaded than in a system performing receive power controlonly.

Receive power can be controlled by adapting the antenna's loadimpedance. The load adaptation may use a circuit that is highlyadaptive, meaning that the receiver must be capable of varying theantenna loading over a wide range. It can also be theoretically shownthat in a system based on coupled resonance, there is no requirement toreadjust antenna frequency tuning when the coupling factor betweenantennas is changing, provided that each antenna is correctly tuned tothe operating frequency, independent of its loading. Thus, the problemof adapting the system to different coupling factors reduces to loadadaptation.

The multiple receiver scenario is more complex since in general thereexist different receivers in different coupling conditions also havingdifferent power demand. An example of a multiple receiver scenario thatmay result e.g. in the wireless desktop IT application described inprevious embodiments is shown in FIG. 5-9.

In a multiple receiver scenario, power and receive antenna loadingcontrol is of greater importance.

One embodiment uses a model compensation technique when there is onlyone receiver, and uses a feedback sensing technique when there is morethan one receiver.

A receiver approaching the transmitter ideally should not negativelyaffect power transmission to other more distant receivers e.g. bysucking off large amount of power or mismatching the transmitter.

FIG. 5-9 shows how power and transfer efficiency control can be used tocompensate the variable coupling factor and to share available poweramong receivers in an equitable manner and according to their demand. Inone embodiment, the devices may be arranged in a coplanar arrangement.

A similar problem may result if two receivers are approaching each otherand start to mutually couple. Load control in the receivers can be usedto manage these different scenarios, e.g, by adjusting the tuning toavoid detuning effects.

The multiple receiver scenario is much more complicated than the singlereceiver scenario. In case of a single receiver, efficiency control isstraightforward. A multiple receiver scenario transfer efficiencycontrol is much more complex and may also use data exchange(communication) between transmitter and receivers to optimally adjustsystem parameters. Efficiency control will also be less effective, asthe system may need to consider the link with lowest coupling factor,thus not being able to improve efficiency in the more favorable links.In other words: a single distant receiver can degrade the overalltransfer efficiency in a multiple receiver scenario.

Licensing issues may also be considered. The use of frequencies forwireless transmission with a power above a certain uncritical levelnormally requires a license and a specific assignment of that frequencyfor this purpose/service.

Frequencies in the so-called ISM bands are exempted from suchregulation. There exist a number of ISM bands in frequency ranges thatcould principally be used for wireless power applications.

For vicinity coupling systems designed to operate over distances say upto 1 m, frequencies in the VLF, LF, or HF spectrum are of particularinterest. Presently there are however only a few ISM bands permittinglicense-exempt operation at increased magnetic field strength levels.

Some of these bands are allocated below 135 kHz (VLF, LF). Anothernarrow band exists in the HF spectrum at 13.56 MHz (+/−3 kHz).

The regulatory norm applicable in these frequency bands defines emissionlimits e.g. in terms of magnetic field strength measured at a specifieddistance from the radiation source. The distance specified by ECC forEurope differs from that specified by FCC for US, thus field strengthlimits cannot easily be compared. At the first glance it looks like thatLF allows for higher emission levels thus being advantageous over HF.However, the magnetic field strength resulting at LF is higher than thatat HF assuming equivalent systems transferring equal power with equalefficiency over the same distance. In theory the field strengthresulting at 135 kHz (LF) is 20 dB higher compared to 13.56 MHz (HF).Present regulations take this fact partially into account. Limits at LFare comparatively more restrictive than those defined for HF.

Moreover, comparing ECC and FCC emission limits taking into accountproposed factors for distance correction make it appear that the FCC isgenerally more restrictive than ECC, though many products used in Europeare also traded and operated in the US (e.g. high power RFID readers).

Establishing a very narrow frequency band at LF (e.g. +/−100 Hz)permitting license exempt operation at increased levels on a world-widebasis may be used in one embodiment. Such allocation would howeverrequire lobbying activity from various stake holder groups of thewireless power and RFID companies, and might require evidence thatwireless power systems would not cause harmful interference to relevantradio services. Similar developments already occurred at 13.56 MHz,where emission limits were increased by almost 20 dB based on pressureof the RFID lobby. This change request was accepted by regulatorybodies, since RFID readers transmit a strong continuous wave componentrequiring very narrow bandwidth.

A primary purpose of frequency regulation is to protect radio servicesfrom mutual interference. There exist however a number of non-radiosystems with limited immunity to electromagnetic radiation such as

-   -   wire bounded communication systems (mainly those using        non-properly shielded lines such as powerline, ADSL, VDSL, etc.)    -   safety critical systems such as cardiac pacemakers    -   security critical systems such as credit cards, etc.

These systems are not specifically protected by frequency regulatorynorms. However, embodiments of the wireless power systems produceessentially non-modulated radiation fields, forming a major advantage inregard to these EMC aspects. The interference potential from modulatedor pulsed emissions such as produced by high power RFID, inductioncooking, etc. is known to be much higher in general.

Beside frequency regulatory norms regulating coexistence of radiosystems, radiation exposure limits have additionally been established toprotect biological being from adverse biological effects. The biologiclimits are set based on thresholds above which adverse health effectsmay occur. They usually also include a safety margin. In the frequencyrange of interest for wireless power applications, radiation is termednonionizing radiation (NIR). One relevant association concerned withnon-ionizing radiation protection is INIRC that was established in 1992.Their function is to investigate the hazards, which are associated withdifferent forms of NIR, to develop international guidelines on NIRexposure limits and to deal with all aspects of NIR protection. TheICNIRP is a body of independent scientific experts consisting of a mainCommission of 14 members, 4 Scientific Standing Committees and a numberof consulting experts. They also work closely together with the WHO indeveloping human exposure limits.

The ICNIRP have produced guidelines for limiting electromagnetic fieldexposure in order to provide protection against known adverse healtheffects [ICN 98]. Various scientific studies have been performedworldwide. Results of these studies were used to determine thresholds atwhich the various adverse health effects could occur. The basicrestrictions are then determined from these thresholds including varyingsafety factors. Basic restrictions and reference levels have beenprovided by INIRC for both:

-   -   General public exposure: exposure for the general population        whose age and health status may differ from those of workers.        Also, the public is, in general, not aware of their exposure to        fields and cannot take any precautionary actions (more        restrictive levels), and    -   Occupational exposure: exposure to known fields allowing        precautionary measures to be taken if required (less restrictive        levels)

The coupling mechanisms through which time-varying fields interact withliving matter may be divided into three categories:

-   -   coupling to low-frequency electric fields results in        reorientation of the electric dipoles present in the tissue    -   coupling to low-frequency magnetic fields results in induced        electric fields and circulating electric currents    -   absorption of energy from electromagnetic fields results in        temperature increase which can be divided into four        subcategories:        -   100 Hz-20 MHz: energy absorption is most significant in the            neck and legs        -   20 MHz-300 MHz: high absorption in the whole body        -   300 MHz-10 GHz: significant local non-uniform absorption        -   >10 GHz: energy absorption occurs mainly at the body surface

The following is a description of the scientific bases that were used byINIRC in determining the basic restrictions for different frequencyranges:

-   -   1 Hz-100 kHz: restrictions are based on current density to        prevent effects on nervous system function    -   100 kHz-10 MHz: restrictions are based on the Specific Energy        Absorption Rate (SAR) to prevent whole-body heat stress and        excessive localized tissue heating as well as current density to        prevent effects on nervous system function    -   10 MHz-10 GHz: restrictions are based solely on SAR to prevent        whole-body heat stress and excessive localized tissue heating

The basic restrictions are based on acute, instantaneous effects in thecentral nervous system and therefore the restrictions apply to bothshort term and long term exposure.

A summary of the biological effects for each frequency range is shownbelow:

Frequencies below 100 kHz:

-   -   Exposure to low frequency fields are associated with membrane        stimulation and related effects on the central nervous system        leading to nerve and muscle stimulation.    -   There is little evidence that magnetic fields have a        tumor-promoting effect and the data is insufficient to conclude        whether these fields promote the growth of currently present        cancerous cells.    -   Laboratory studies have shown that there is no established        adverse health effects when induced current density is at or        below 10 mA/m².

Frequencies above 100 kHz:

-   -   Between 100 kHz and 10 MHz, a transition region occurs from        membrane effects to heating effects    -   Above 10 MHz the heating effects are dominant    -   Temperature rises of more than 1-2° C. can have adverse health        effects such as heat exhaustion and heat stroke    -   A 1° C. body temperature increase can result from approximately        30 minutes exposure to an electromagnetic field producing a        whole-body SAR of 4 W/kg.    -   Pulsed (modulated) radiation tends to produce a higher adverse        biological response compared to CW radiation. An example of this        is the “microwave hearing” phenomenon where people with normal        hearing can perceive pulse-modulated fields with frequencies        between 200 MHz-6.5 GHz

For health/biological limits, all organizations and regulatory bodiesthroughout the world agree upon the scientific findings that a wholebody SAR of 4 W/kg is the threshold at which adverse health effects canoccur. They also agree that for the basic restrictions, a safety factorof 10 should be used, so that the basic restrictions on whole body SARshould not be any higher than 0.4 W/kg for occupational exposure and0.08 W/kg for general public exposure.

The different standards disagree is in regard to the H-field referencelevels for human exposure. The IEEE provides the most non-restrictivelimits based on a variety of scientific studies. The IEEE limits aregenerally accepted in north America (as they are also approved by ANSI)as well as NATO. The most restrictive levels are provided by ICNIRP as alarge safety factor is taken into consideration for these limits.Japanese proposed limits are somewhere between the IEEE and ICNIRPlimits. There is no evidence showing that the limits proposed by theIEEE C95.1 standard would still provide dangerous exposure levels.

In all cases, the human exposure H-field reference levels can beexceeded, as long as a wholebody SAR of 0.08 W/kg is not exceeded.

In the embodiments for wireless power applications for vicinitycoupling, magnetic field strength is generally below IEEE/NATO limits.It may however exceed ICNIRP limits at positions close enough totransmit or receive antennas. As magnetic fields in the near field of anantenna increase with the 3rd power of distance, there is always aradius where ICNIRP limits may be exceeded, also depending on antennasize, performance, and power/currents.

In contrast to frequency regulatory limits, radiation exposure limits donot specify a distance from the radiation source where field strengthhas to be compliant. They have to be interpreted as applying to all lociwhere biological matter may be located, which makes definition ofcompliance fuzzy.

This problem is however not unique to wireless power but is also anissue of other systems such as RFID systems, induction cooking,induction welding, etc. Such systems require judgment and certificationby a competent body.

Concluding, radiation exposure is an issue requiring seriousinvestigation not least because of the increasing phobia ofelectromagnetic radiation among a majority of people, especially inEurope. It is considered a big challenge and a potential risk ofvicinity coupling wireless power mainly in mass market applications.

Beyond that is user perception: some people may not like to becontinuously exposed to AC magnetic fields e.g. while working at theiroffice desk, independently of their actual strength relative toestablished limits.

One embodiment discloses transmission activity control. Devices are onlycharged during time of absence (e.g. during the night) using a humanpresence detector (e.g. microwave movement or infrared sensor or both,or other methods). During time of presence of a human being in theproximity or vicinity of the transmit antenna, power is switched-off orreduced to lower levels.

The devices may provide receive a power level indicator to ensure thatthey are kept in a position/orientation such to receive sufficient powerfrom the transmitter. This indicator function may be preserved alsoduring non-active times or in times of reduced power mode.

This may be accomplished through the following alternative methods:

-   -   periodic very low duty cycle activation of transmitter using        soft power ramp-up or ramp-down in order to avoid EMI problems        (e.g. ‘clicks’ in devices having an audio interface such as        phones, speaker systems, etc.)    -   continuous transmission at reduced power levels but sufficiently        high to be detected by the device to control the level indicator

Office equipment (personal computers, monitors, fax machines, scanners,copiers, printers, etc.) account for a large proportion of electricityconsumption in the tertiary sector. In the context of internationalcommitments, particularly in the area of climate change (notably theKyoto Protocol), and given its objectives in such areas as sustainabledevelopment, the energy efficiency initiatives take on specialsignificance. This coordinated labelling program (known as ENERGY STAR)enables consumers to identify energy-efficient appliances and shouldtherefore result in electricity savings that will help not only toprotect the environment but also to ensure the security of the energysupply. The program may also help to encourage the manufacturing andsale of energy-efficient products.

Energy star guidelines have already been implemented and may also affectto a certain degree future market introduction of wireless powerproducts.

In the last years, a number of companies also supported by academia havestarted research and development activities in the area of wirelesspower mainly in regard to applications in the consumer market sector. Amajority of these initiatives focus on solutions using inductivecoupling as the technological basis. Typical solutions are inductivecharging pads designed for contactless charging of a single or multipledevices. In all these solutions power is transferred over very shortdistances e.g, millimeters or centimeters. Using the terminology of theRFID world, these systems/solutions fall into the category of proximitycoupling systems.

Similarly to RFID applications, a proximity coupling solution forwireless powering and charging is not always practical and cannotprovide the flexibility/mobility and degree of freedom expected byusers. This is the rationale behind power transmission over largerdistances in the range of decimeters or even metres. Using again RFIDterminology, such systems may be associated to the category of vicinitycoupling systems.

The price for more range and flexibility/mobility is generally

-   -   higher radiation levels    -   higher device integration impact in terms of complexity and        costs (BOM)    -   lower transferable power    -   lower transfer efficiency

In Table 6-1 below, proximity coupling and vicinity coupling is comparedwith respect to selected aspects that are considered relevant.

TABLE 1 Proximity coupling Vicinity coupling Basis solution Wirelesspower enabled Wireless power enabled devices devices must be positionedon can be positioned in proximity or an inductive pad (virtually zerovicinity of a power base (short range but contactless) range) Basictechnology Classical inductive coupling Magnetic coupled resonance withhigh coupling factor and (inductive coupling with high Q- low Qresonance resonance to compensate for low coupling factor) Energyefficiency Higher Lower Close to those of corded Depending on solutionpossible position/distance of device (60 to 90%) (0.5-90%) Radiationexposure Lower Higher EMC Issues No particular problems Tightconstraints for expected for smart transferable power and charging padsthat can range by radiation exposure automatically detect loads limitsand control power Potential of interference of accordingly. otherssystems susceptible to Less constraints on strong magnetic fields (nottransferable power exhaustively tested yet) May require more publicconvincing May require special means to control field strength in humanpresence to get market acceptance

TABLE 2 Frequency regulatory & Lower Higher standardisation efforts Canbe designed more May require new regulations easily to meet existing andstandards specific to regulations & standards wireless power Potentialto be supported May require some lobbying by a broad stakeholder effortsto get approval of group thus becoming a frequency authorities mainstream standard May require standardised wireless power interface andfrequency to achieve device compatibility Standardisation efforts mightbe torpedoed by stakeholders of proximity systems Implementation costsLower Higher (BOM impact) Very simple RX solutions High Q-factorrequired possible leading to higher voltages/ Lower Q-factor in basecurrents (physically larger and RX components needed) Tuning in RX notPrecise tuning in base and compulsory RX compulsory Wide-rangeadaptability in RX required Impact on device Lower Higher designSolutions with very low Larger/more bulky antennas impact on devicesize/from & likely more complex factor and internal circuitryelectronics required possible More design constraints to preserve highQ-factor Device positioning Lower Higher degree of freedom No solutione.g. for Attractive solutions e.g. for wireless desktop wireless desktopapplications applications (e.g. for charging keyboard, mouse) Multipledevice Limited Less limited powering/charging depending on size of padand depending on available transmit available transmit power power

TABLE 3 Frequency regulatory & Lower Higher standardisation efforts Canbe designed more May require new regulations easily to meet existing andstandards specific to regulations & standards wireless power Potentialto be supported May require some lobbying by a broad stakeholder effortsto get approval of group thus becoming a frequency authorities mainstream standard May require standardised wireless power interface andfrequency to achieve device compatibility Standardisation efforts mightbe torpedoed by stakeholders of proximity systems Implementation costsLower Higher (BOM impact) Very simple RX solutions High Q-factorrequired possible leading to higher voltages/ Lower Q-factor in basecurrents (physically larger and RX components needed) Tuning in RX notPrecise tuning in base and compulsory RX compulsory Wide-rangeadaptability in RX required Impact on device Lower Higher designSolutions with very low Larger/more bulky antennas impact on devicesize/from & likely more complex factor and internal circuitryelectronics required possible More design constraints to preserve highQ-factor Device positioning Lower Higher degree of freedom No solutione.g. for Attractive solutions e.g. for wireless desktop wireless desktopapplications applications (e.g. for charging keyboard, mouse) Multipledevice Limited Less limited powering/charging depending on size of padand depending on available transmit available transmit power power

Although only a few embodiments have been disclosed in detail above,other embodiments are possible and the inventors intend these to beencompassed within this specification. The specification describesspecific examples to accomplish a more general goal that may beaccomplished in another way. This disclosure is intended to beexemplary, and the claims are intended to cover any modification oralternative which might be predictable to a person having ordinary skillin the art. For example, other sizes, materials and connections can beused. Other structures can be used to receive the magnetic field. Ingeneral, an electric field can be used in place of the magnetic field,as the primary coupling mechanism. Other kinds of antennas can be used.Also, the inventors intend that only those claims which use the-words“means for” are intended to be interpreted under 35 USC 112, sixthparagraph. Moreover, no limitations from the specification are intendedto be read into any claims, unless those limitations are expresslyincluded in the claims.

Where a specific numerical value is mentioned herein, it should beconsidered that the value may be increased or decreased by 20%, whilestill staying within the teachings of the present application, unlesssome different range is specifically mentioned. Where a specifiedlogical sense is used, the opposite logical sense is also intended to beencompassed.

What is claimed is: 1-40. (canceled)
 41. An apparatus configured totransmit power via a magnetic field, the apparatus comprising: anantenna circuit configured to inductively transmit power via themagnetic field at a magnetic field strength level sufficient to chargeor power a receiver device; a detection circuit configured to detect apresence of a living being within a region of the magnetic field inwhich power is inductively transmitted at the magnetic field strengthlevel; and a controller configured to adjust the magnetic field strengthlevel in response to detecting the presence of the living being withinthe region of the magnetic field.
 42. The apparatus of claim 41, furthercomprising a driver circuit configured to drive the antenna circuit at afrequency substantially equal to a resonant frequency of the antennacircuit.
 43. The apparatus of claim 41, wherein the detection circuit isconfigured to detect the presence of the living being based on microwavedetection.
 44. The apparatus of claim 41, wherein the detection circuitcomprises an infrared sensor configured to detect the presence of theliving being.
 45. The apparatus of claim 41, wherein the controller isconfigured to reduce the magnetic field strength level to at least oneof a lower magnetic field strength level or substantially zero.
 46. Theapparatus of claim 0, wherein the lower magnetic field strength levelcorresponds to a level configured to avoid biological harm to the livingbeing.
 47. The apparatus of claim 0, wherein the lower magnetic fieldstrength level is based on a target specific energy absorption rate(SAR).
 48. The apparatus of claim 41, wherein the region corresponds toa near-field of the antenna circuit.
 49. A method of transmitting powervia a magnetic field, the method comprising: inductively transmittingpower via the magnetic field at a magnetic field strength levelsufficient to charge or power a receiver device; detecting a presence ofa living being within a region of the magnetic field in which power isinductively transmitted; and adjusting the magnetic field strength levelin response to detecting the presence of the living being within theregion of the magnetic field.
 50. The method of claim 49, whereinadjusting the magnetic field strength level comprises reducing themagnetic field strength level to at least one of a lower magnetic fieldstrength level or substantially zero.
 51. The method of claim 50,wherein the lower magnetic field strength level corresponds to a levelconfigured to avoid biological harm to the living being.
 52. The methodof claim 50, wherein the lower magnetic field strength level is based ona target specific energy absorption rate (SAR).
 53. The method of claim49, wherein detecting the presence of the living being comprisesdetecting the presence of the living being based on microwave detection.54. The method of claim 49, wherein detecting the presence of the livingbeing comprises detecting the presence of the living being via aninfrared sensor configured to detect the presence of the living being.55. An apparatus configured to transmit power via a magnetic field, theapparatus comprising: means for inductively transmitting power via themagnetic field at a magnetic field strength level sufficient to chargeor power a receiver device; means for detecting a presence of a livingbeing within a region of the magnetic field in which power isinductively transmitted; and means for adjusting the magnetic fieldstrength level in response to detecting the presence of the living beingwithin the region of the magnetic field.
 56. The apparatus of claim 55,wherein the means for adjusting the magnetic field strength levelcomprises means for reducing the magnetic field strength level to atleast one of a lower magnetic field strength level or substantiallyzero.
 57. The apparatus of claim 56, wherein the lower magnetic fieldstrength level corresponds to a level configured to avoid biologicalharm to the living being.
 58. The apparatus of claim 56, wherein thelower magnetic field strength level is based on a target specific energyabsorption rate (SAR).
 59. The apparatus of claim 55, wherein the meansfor detecting the presence of the living being comprises means fordetecting the presence of the living being based on microwave detection.60. The apparatus of claim 55, wherein the means for detecting thepresence of the living being comprises an infrared sensor configured todetect the presence of the living being.